So i read the wikipedia page on boltzman brains, saying that self-aware observers are probably spontaneous fluctuations. It unsettled me a bit. I googled for some reasons as why it might be incorrect, and I couldn't find any reasonable disproofs. Some pages said that evolution allowed life and complexity to evolve without a spontaneous apparition, but it seems evolution in our universe would require a massive entropy fluctuation, which means the argument is flawed.

Does anyone know of any arguments against boltzman brains?

It does seem bizzare to ask this considering i'm convinced that i'm only a temporary fluctuation, doesn't it.

What does it mean to be "self aware"? How would one distinguish this from the mere "appearance of self awareness"? As you push on the question, you may reach enlightenment as to why it is neither correct nor incorrect.

Then, let go of the idea of self-awareness, and generalize. Any quantum configuration could have spontaneously appeared (provided that certain constraints, such as mass and energy, are satisfied). Entropy is not an absolute, it is a statistic; unlikely doesn't mean impossible (though I wouldn't bet a lottery ticket on it!) Point is, self-awareness is nothing special wrt the underlying premise.

After you grok this, ask the new question that should be precipitated.

Jose

Order of the Sillies, Honoris Causam - bestowed by charlie_grumbles on NP 859 * OTTscar winner: Wordsmith - bestowed by yappobiscuts and the OTT on NP 1832 * Ecclesiastical Calendar of the Order of the Holy Contradiction * Heartfelt thanks from addams and from me - you really made a difference.

If our universe is in thermal equilibrium, with any low-entropy structures arising as the result of random fluctuations, then most observers would be bolzmann brains.

That's a big if, and that's an important qualifier.

The good news is: you and I do not appear to be bolzmann brains. Of course it's impossible to prove with certainty, but we can force experiences that a bolzmann brain would be very unlikely to have. Like, just go outside. If the outside looks as you remember it, you're probably not a bolzmann brain.

The argument then goes that you and I are somewhat representative observers (a debatable assumption), hence most observers are not bolzmann brains, hence our universe is not a universe that's in thermal equilibrium for most of its existence. The thought experiment is meant to tell us things about cosmological models, not about ourselves.

Yeah, it's supposed to demonstrate a problem with a model of a universe in which the Big Bang was the result of a statistical fluctuation. In such a model, it would indeed be far more likely to get a brain (or whatever) popping up out of a random fluctuation than an entire low entropy universe. So that's probably not a good explanation for the Big Bang.

I'm a bit burnt out right now so these are not the clearest thoughts, but it seems intuitively wrong to me that specifically a fully-formed brain having (illusory) experiences or memories of a universe like ours is more likely to randomly arise than just any old low-entropy configuration of the universe from which could then evolve states of the universe in which some (un)lucky parts are such brains but most of it is just a diffuse plasma.

It also reminds me a bit of arguments from design, and counterarguments to them. The creationist looks as the handful of carefully selected complex bits of the local universe, filtered out from the diffuse plasma that is most of the rest of it, and says "no way that could happen by chance in a universe that just popped into existence for no reason! There must be an intelligent God behind it all!", and a counterargument goes that we're then being asked to believe that not just a mechanistic universe happens to exist for no reason, but that instead a hyperintelligent superpowerful person (God) just happened to exist for no reason, and then decided to create a much simpler mechanistic universe, some parts of which filter out some temporary complexity maybe slightly comparable to the being whose existence we're being asked to accept as just a brute fact without need for explanation.

In short, God is greater than the universe. And yet, why do we argue that God needs less of an explanation than the universe does? We can argue that God exceeds the ability of our limited human minds to comprehend, but that is an argument for the explanation of God to be greater, not lesser.

I'm not sure exactly what point you're making Ijuin, as I was basically referring to the exact thing you just said, and comparing that to the topic of Bolztman brains. A brain that thinks it's perceiving a universe popping into existence seems more comparable to a god intent on creating a universe popping into existence, than either do to some random low-entropy configuration of the universe randomly happening and then evolving in a way that gives rise in some small places to a few things capable of perception and intent and so on.

gvnbm2018 wrote:Some pages said that evolution allowed life and complexity to evolve without a spontaneous apparition, but it seems evolution in our universe would require a massive entropy fluctuation, which means the argument is flawed.

The second law of thermodynamics only describes the evolution of systems over time. It says nothing about a system's initial state. There's no reason a system can't start in a state of very low entropy - indeed there's every evidence that ours did.

Secondly, only isolated systems rise in entropy over time. Life is an entirely natural and deterministic mechanism that results in local entropy lowering over time, sometimes precipitously. That's essentially the most interesting thing about it, alongside the whole consciousness thing.

Therefore there's no reason to think that, in our particular universe, at this particular time, boltzman brain consciousnesses will outnumber conscious ones, and every reason to think that the world is, in fact, how it seems to be.

Pfhorrest wrote:I'm a bit burnt out right now so these are not the clearest thoughts, but it seems intuitively wrong to me that specifically a fully-formed brain having (illusory) experiences or memories of a universe like ours is more likely to randomly arise than just any old low-entropy configuration of the universe from which could then evolve states of the universe in which some (un)lucky parts are such brains but most of it is just a diffuse plasma.

There are some problems with the model, yeah. For one, even if a Boltzmann brain did pop into existence, it would necessarily exist for a very short period of time. It's not self sustaining, unless we happen to have a great deal more complexity pop into existence, and ignoring anti-matter annihilation*. The same is not true of more traditional models of life.

It also relies on very, very large numbers to be persuasive. Sure, enough random configurations in a large enough space/time can eventually give you a high likelihood of an event arising. However, said events are still extremely rare. It would be fairly odd for one Boltzmann brain to converse with another, simply because both are so rare. This would not be true for a deterministic explanation for life. This would significantly tip the scales against a "we are all Boltzmann brains" argument.

We'd also expect, if we were Boltzmann brains, to have a vast bias towards simplicity. Size/complexity rapidly decreases the likelihood**. Odds of a minimal brain popping into existence are not really the same as odds of an average human brain popping into simplicity. Instead, we see brains distributed in a manner that seems consistent with traditional causal explanations. Taken together, the above extreme improbabilities ought to be quite sufficient to rule out any idea that we're Boltzmann brains.

*The anti-matter bit is sufficient to rule out quantum fluctuation, I think. **If I'm not mistaken, the spontaneous appearance of a single human-scale brain would be wildly improbable anywhere in the entire universe over it's entire history. The importance of scale/complexity happens to coincide nicely with a diefic/superintelligent explanation being far less likely than a human one. Even if random appearance were relied upon to explain life and intelligence, we still ought to expect lesser life forms to precede larger/more complex variants, rather than a deific model.

I don't think anyone is proposing that you and I and this entire community of humans might all be separate Boltzman brains that all independently popped into being and are talking to each other somehow. Just that for you, any individual thinker considering the argument, odds are that you are just a Boltzman brain who merely thinks, for this brief fleeting moment that you exist, that you are a normal human on a planet full of humans who has been around and thinking and experiencing things for many years, while in reality all of that world you think you inhabit, and all of its history, is just a false memory that you were spontaneously formed with right now, and nothing and nobody else has ever really existed.

I'll ignore all the unrelated and unscientific drivel about gods for now..

Pfhorrest wrote:I'm a bit burnt out right now so these are not the clearest thoughts, but it seems intuitively wrong to me that specifically a fully-formed brain having (illusory) experiences or memories of a universe like ours is more likely to randomly arise than just any old low-entropy configuration of the universe from which could then evolve states of the universe in which some (un)lucky parts are such brains but most of it is just a diffuse plasma.

The important difference is that a brain is a lot smaller. Let's do a very rough ballpark estimate.

A human brain including memories requires ~10^27 atoms in just the right low-entropy configuration.

An early universe that can evolve into our observable universe requires ~10^80 atoms in just the right low-entropy configuration.

If the chance for a suitable low-entropy atom to appear from the soup right now is p, then those chances are p^(10^27) vs p^(10^80). Let's divide them:p^(10^27) / p^(10^80) = (1/p)^(10^80 - 10^27) ~= (1/p)^(10^80)As p is very small, a bolzmann brain is way more than 2^(10^80) times more likely to happen.

This difference has so many orders of magnitude that I'm confident that pursuing more accurate estimates won't change the answer.

elasto wrote:Life is an entirely natural and deterministic mechanism that results in local entropy lowering over time, sometimes precipitously.

There's nothing special about life with regards to entropy. There are plenty of non-living systems that can lower local entropy (I think I have one of those in my kitchen), but (both living and non-living) systems can only do so by raising entropy somewhere else, so the total entropy will (on average) keep rising.

elasto wrote:There's no reason a system can't start in a state of very low entropy - indeed there's every evidence that ours did.

You can't talk about an initial state unless you accept the arrow of time as a fundamental ingredient of your theory. Looking through time in one arbitrary direction, picking a point and calling it the "start" isn't going to lead to good conclusions.Besides, nobody knows if the big bang was the earliest point of time in our universe. Some plausible cosmological models say that is wasn't; some say that the universe is infinite into both past and future. We have no evidence either way.

pforrest wrote:I don't think anyone is proposing that you and I and this entire community of humans might all be separate Boltzman brains that all independently popped into being and are talking to each other somehow.

Certainly not. I am a bolzmann brain and you're all randomly generated memories that don't exist. I'll pop out of existence soon, but more brains will follow, and eventually one will remember you as well.

Tub wrote:A human brain including memories requires ~10^27 atoms in just the right low-entropy configuration.

An early universe that can evolve into our observable universe requires ~10^80 atoms in just the right low-entropy configuration.

It basically comes down to these two numbers.

That said, a universe can mechanistically produce a helluva lot more than one brain, whereas the Boltzmann brain incident will only ever produce the one. So, with survivorship bias factored in, we should still not be surprised to see the former.

Also, we don't need *this* particular universe. We just need any universe that can support life. This is a lower bar, though how much lower is sort of up for debate.

To put a bit of context to the idea, the question of why the universe began in an extremely low entropy state is a difficult one and has been pondered for a long time. Older theories of cosmology held the universe to be eternal and essentially static, but once convincing evidence for the Big Bang was found, it had to be answered. The reason entropy always tends to increase is that there are far more microscopic configurations that look like high entropy states than low entropy ones. Actually, that's more or less the definition of entropy. This also gives us an arrow of time, because entropy was very low in the past, so as the universe approaches equilibrium, we get clear asymmetry between past and future.

But most universes do not have one point in time with super low entropy, by the same argument. Indeed, statistically, we should expect the past to have higher entropy for the same reason we expect the future to have higher entropy. What caused this? Why does our universe seem to have such extremely unusual boundary conditions?

One early answer was that the universe really was eternal, or at least very old, and that the present state of expansion is the result of a colossal and extremely rare non-equilibrium event in which, by chance alone, the entropy of one patch of the universe radically dropped. The time you would expect to have to wait before something like that happened is enormous, but if the universe is eternal, then it's still bound to happen (indeed, bound to happen infinitely many times). So maybe there is no mystery at all.

However, if that were the case, then we would also expect other, smaller fluctuations to happen more frequently. Indeed we do--if the universe really does last forever, we can expect just about any possible event to occur, with the less probable ones happening less often. Rarely, but occasionally, such a fluctuation might include the production of something briefly conscious or simulating consciousness, and this would happen many orders of magnitude more often than the proposed creation of the universe. Therefore, by this logic, it is many orders of magnitude more likely that I am such a "Boltzmann brain" and that the universe I imagine doesn't even exist. That is a troubling conclusion, and it demonstrates the weakness of this idea.

More modern ideas of cosmogeny vary tremendously, but some of them still fall into the same trap, which is why the thought experiment has hung around. Any hypothesis that relies on extremely large time scales needs to deal with this.

elasto wrote:Life is an entirely natural and deterministic mechanism that results in local entropy lowering over time, sometimes precipitously. That's essentially the most interesting thing about it, alongside the whole consciousness thing.

There's nothing special about life with regards to entropy. There are plenty of non-living systems that can lower local entropy (I think I have one of those in my kitchen)

Why say there's nothing special about life with regards to entropy-lowering, and then give an example of something life created that lowers entropy?

Besides, I said life was interesting because it lowered local entropy; I never said it was unique for it. Life is, after all, made of 'non-life' building blocks - it's an emergent phenomenon not a fundamental one - so that would be absurd. But if you looked at another planet and saw it was in a low entropy state, wouldn't your conclusion be that most likely life was on there?

That's why life is interesting and worth preserving, even before you get into the whole consciousness thing. I mean, if we created nanobots that went out into the galaxy converting other planets into more nanobots that did the same thing, they would in every sense that matters be alive, but if they lacked consciousness it would be a rather cold and depressing future for our galaxy.

You can't talk about an initial state unless you accept the arrow of time as a fundamental ingredient of your theory.

Aren't we assuming the second law of thermodynamics to be true here? If you do, then an arrow of time is an unavoidable conclusion: The future is in the direction of increasing entropy, and brains can only remember the past and not the future (regardless of whether time actually 'flows' or not).

And if you throw out the second law then of course all bets are off, including any rationalisation over how probable Boltzman brains are.

Besides, nobody knows if the big bang was the earliest point of time in our universe. Some plausible cosmological models say that is wasn't; some say that the universe is infinite into both past and future. We have no evidence either way.

That's irrelevant. By 'start of the universe' I mean 'the furthest back in time that physics can probe'. Anything beyond that is unscientific to speculate about and does not change the argument.

A human brain including memories requires ~10^27 atoms in just the right low-entropy configuration.

An early universe that can evolve into our observable universe requires ~10^80 atoms in just the right low-entropy configuration.

...

As p is very small, a bolzmann brain is way more than 2^(10^80) times more likely to happen.

I refer you back to what Eebster said:

Eebster the Great wrote:Yeah, it's supposed to demonstrate a problem with a model of a universe in which the Big Bang was the result of a statistical fluctuation. In such a model, it would indeed be far more likely to get a brain (or whatever) popping up out of a random fluctuation than an entire low entropy universe. So that's probably not a good explanation for the Big Bang.

When Relativity predicts a singularity within a black hole, the most likely explanation is that the theory isn't quite right yet - and, indeed we know it's not since it doesn't mesh with Quantum theories which we have even stronger evidence for.

Likewise you can't compare a 10^27 brain with a 10^80 universe without a theory of how likely a low entropy 10^80 universe is to arise. The BB argument suggests it's much more likely than some current theories would propose - and therefore it's likely that any such theory is wrong rather than that I am a BB and you are all about to wink out of existence.

elasto wrote:But if you looked at another planet and saw it was in a low entropy state, wouldn't your conclusion be that most likely life was on there?

You snuck in a claim here, implying that earth has the lowest entropy of the planets in the solar system, because there's life on it. As far as I can see, our ability to lower entropy is much more localized than planet scale, and I see no reason to believe that earth's entropy is significantly lower than the entropy of the uninhabited planets. So I'm going to put a [citation needed] on your claim.

elasto wrote:Aren't we assuming the second law of thermodynamics to be true here? If you do, then an arrow of time is an unavoidable conclusion: The future is in the direction of increasing entropy, and brains can only remember the past and not the future (regardless of whether time actually 'flows' or not).

The arrow of time is certainly measurable right here and right now, and it has existed for ~13 billion years; the question is whether it's a fundamental law of physics or just a local irregularity. There may be epochs in our universe where there is no arrow of time, or there may be epochs where the arrow of time points in the other direction.

I like the following analogy: right now, you're feeling an arrow of direction, where moving up and moving down is different. But that arrow of direction will change as you move around the earth, and it'll disappear entirely if you move far enough away. It's not a fundamental law of physics, it's just a local irregularity caused by being close to a massive object.Likewise, the arrow of time is a local irregularity caused by being close to a low-entropy state. It's probably not fundamental, nor does it have to be valid everywhere, nor does it always have to point in the same direction.

If you assume that the universe had a starting configuration, that'll lead you to discount any cosmological model with multiple arrows of time. It'll also lead you to discount any cosmological models that are infinite in both time directions. The assumption of an initial state is not a helpful one.

elasto wrote:That's irrelevant. By 'start of the universe' I mean 'the furthest back in time that physics can probe'. Anything beyond that is unscientific to speculate about and does not change the argument.

It is possible to make testable predictions about unobservable parts of our universe. Don't dismiss cosmology as unscientific just because it requires extrapolation.

Tub wrote:You snuck in a claim here, implying that earth has the lowest entropy of the planets in the solar system, because there's life on it. As far as I can see, our ability to lower entropy is much more localized than planet scale, and I see no reason to believe that earth's entropy is significantly lower than the entropy of the uninhabited planets. So I'm going to put a [citation needed] on your claim.

Huh? Just take the existence of an oxygen atmosphere for starters. That's on a planetary scale and, while some non-living processes can produce it, were we to detect it in high amounts on a planet orbiting a distant star would be a big signpost that life might be in play.

The arrow of time is certainly measurable right here and right now, and it has existed for ~13 billion years; the question is whether it's a fundamental law of physics or just a local irregularity. There may be epochs in our universe where there is no arrow of time, or there may be epochs where the arrow of time points in the other direction.

I agree.

Likewise, the arrow of time is a local irregularity caused by being close to a low-entropy state. It's probably not fundamental, nor does it have to be valid everywhere, nor does it always have to point in the same direction.

I agree.

Can you explain why you're bringing that up in relation to the argument about BB's though?

We know that time isn't fundamental. Relativity claims that space-time is fundamental, but that probably isn't true either.

If you assume that the universe had a starting configuration, that'll lead you to discount any cosmological model with multiple arrows of time. It'll also lead you to discount any cosmological models that are infinite in both time directions. The assumption of an initial state is not a helpful one.

By 'starting configuration', I mean 'probing as far back into the past as we can via physics experiments'. We can't probe any further back than that by definition. Don't infer from me saying 'starting configuration' that that implies anything about the nature of time itself. The multiverse might be eternal - indeed it's hard to imagine how it couldn't be (how can something arise out of nothing?) - so that's not what I'm referring to when I speak of our universe's starting configuration.

It is possible to make testable predictions about unobservable parts of our universe. Don't dismiss cosmology as unscientific just because it requires extrapolation.

Um, assuming by 'unobservable' we mean 'those regions of the multiverse that have no causal connectivity with ours' then you can't test any predictions about them by definition.

It places us in the realms of philosophy not science; which is not to say it's valueless - it's still very interesting, and the unscientific parts of life are some of the bits with the most meaning - it's just that it can't credibly be claimed to be attackable via the scientific method.

For example, the BB argument is a philosophical one, not a scientific one, yet it still has something valueable to say. So, an idea being 'unscientific' does not mean it's worth simply dismissing...

The entropy of a planet is mostly going to depend on the temperature and composition of its interior. Any living things on the surface are irrelevant to that calculation. In fact, since living things tend to dump lots of thermal energy into their surroundings, they probably increase the entropy of the surface of the planet, not decrease it. In the long run, global warming will surely outweigh everything else humans have done put together anyway.

But living things themselves are relatively low entropy. The entropy of my insides does not increase appreciably over time. We also build low entropy things, like crystals and refrigerators and MRI machines. I think that's what Tub meant.

Eebster the Great wrote:Yeah, it's supposed to demonstrate a problem with a model of a universe in which the Big Bang was the result of a statistical fluctuation. In such a model, it would indeed be far more likely to get a brain (or whatever) popping up out of a random fluctuation than an entire low entropy universe. So that's probably not a good explanation for the Big Bang.

This is the heart of the matter. Boltzman Brains are an argument used against certain models, it is not "saying that self-aware observers are probably spontaneous fluctuations." I haven't checked the wiki so it may be that things are misleading there.

LE4dGOLEM: What's a Doug?Noc: A larval Doogly. They grow the tail and stinger upon reaching adulthood.

There's a few things about this that bug me - can someone enlighten me?

The contention seems to be that, if the existence of the universe depended on a random fluctuation of total entropy, then BBs, absurd as they are, are more likely than actual brains. However...

What does it mean when you talk about entropy and randomness prior to the existence of the universe? How do these terms have any meaning when referring to a dimensionless point-source?

Whilst some sort of random consciousness seems plausible, configurations that would allow a BB (such as mine) to have memories and knowledge consistent with a non-BB would be highly unlikely, and would imply the existence of an untold number of more 'primitive' BBs (e.g. if there's only one entrant to a lottery, it would be highly unlikely that the lottery would be won. Therefore, if someone won the lottery, we can assume with reasonable confidence that there was more than one entrant).

What am I missing?

How can I think my way out of the problem when the problem is the way I think?

1, yes, all of the prior probability talk is for models that embed the observable universe into a larger universe, like an inflationary multiverse. (not an everett many worlds multiverse.) It's also possible to consider BB in a more limited model that says nothing about the likelihood of the universe, just about what is likely within the universe.

2, yes, it's very unlikely, but if your universe model includes an infinite duration spent just living at thermal equilibrium having thermal fluctuations, then however unlikely your BB is more likely than an OO. infinity * small number > big number

doogly wrote:2, yes, it's very unlikely, but if your universe model includes an infinite duration spent just living at thermal equilibrium having thermal fluctuations, then however unlikely your BB is more likely than an OO. infinity * small number > big number

Okay - but would I be right in saying we would have to assume that there must have been many trillions of BBs in order to statistically allow for a BB as complicated as mine? (a whole bunch of consistent memories - consistent with something that never existed - including some fair chunks of Shakespeare and a relatively coherent understanding of science and history).

How many BBs are required before OO becomes problematically more likely? After all, OO doesn't imply a high degree of 'order' occurred, so much as patches of low and high entropy, and those patches can still display random distribution, just at a larger scale - is that right?

How can I think my way out of the problem when the problem is the way I think?

When we speak of the probability of a BB vs an OO, don’t forget that we are speaking of the de novo origin of one—if that mind reproduces and thus generates a community or ecosystem of its kind, then that still counts as a single origin—e.g. there is one origin of homo Sapiens despite over a hundred billion individual humans having existed to date.

ijuin wrote:When we speak of the probability of a BB vs an OO, don’t forget that we are speaking of the de novo origin of one—if that mind reproduces and thus generates a community or ecosystem of its kind, then that still counts as a single origin—e.g. there is one origin of homo Sapiens despite over a hundred billion individual humans having existed to date.

I may have misunderstood, but I've always assumed that BBs are only meant to last for a moment.

How can I think my way out of the problem when the problem is the way I think?

The thing is, brains tend to be significantly smaller than the entire universe. Ultimately, this is an argument about entropy, and a low entropy universe is much, much less probable than a low entropy brain no matter how it is arranged. Consider that in reality, your extremely improbable brain did evolve in the process of the universe approaching thermodynamic equilibrium; that is, the apparently stupendously unlikely creation was just a tiny eddy in the larger churning waters of the universe. There is no interpretation in which the entire universe arising out of a random fluctuation is more probable than a single mind.

The thing is, brains tend to be significantly smaller than the entire universe. Ultimately, this is an argument about entropy, and a low entropy universe is much, much less probable than a low entropy brain no matter how it is arranged. Consider that in reality, your extremely improbable brain did evolve in the process of the universe approaching thermodynamic equilibrium; that is, the apparently stupendously unlikely creation was just a tiny eddy in the larger churning waters of the universe. There is no interpretation in which the entire universe arising out of a random fluctuation is more probable than a single mind.

But can we reasonably be talking about a single mind, given the elaborate, consistent, but completely fictional history contained in, e.g., mine? It's like setting off a bomb in a junkyard, and not only creating an airplane, but an airport, custom officers, security, runways, supporting infrastructure and manufacturers, and so on. How many bombs in how many junkyards do we need to set off before that becomes a plausible result? And at what point, does that number become less likely than an anti-entropic, essentially unstructured and disorganised, creation event?

How can I think my way out of the problem when the problem is the way I think?

That's why I claim life is special. It didn't take a bomb to create our entire civilisation including aircraft, runways, and a TSA enforcing a 100ml limit on liquids, 'all' it took was a relatively small (but still highly unlikely) amount of randomness producing a self-replicating molecule, and the ongoing luck for that molecule not to die away. And, theoretically, from that first molecule we could spread out to alter the fate of the galaxy if not the universe.

Sure, it's true that life has an insignificant effect on the sum total of entropy even locally - however that's a different thing to saying it has no meaningful effect. In so much as anything can be said to have meaning, it has an effect which is measurable from even light-years away - and by far the most interesting (and worrying) discovery on another planet would be living things...

The thing is, brains tend to be significantly smaller than the entire universe. Ultimately, this is an argument about entropy, and a low entropy universe is much, much less probable than a low entropy brain no matter how it is arranged. Consider that in reality, your extremely improbable brain did evolve in the process of the universe approaching thermodynamic equilibrium; that is, the apparently stupendously unlikely creation was just a tiny eddy in the larger churning waters of the universe. There is no interpretation in which the entire universe arising out of a random fluctuation is more probable than a single mind.

But can we reasonably be talking about a single mind, given the elaborate, consistent, but completely fictional history contained in, e.g., mine? It's like setting off a bomb in a junkyard, and not only creating an airplane, but an airport, custom officers, security, runways, supporting infrastructure and manufacturers, and so on. How many bombs in how many junkyards do we need to set off before that becomes a plausible result? And at what point, does that number become less likely than an anti-entropic, essentially unstructured and disorganised, creation event?

Of course we're talking about a single mind. You can't claim to have independent observations of other things besides your mind, can you?

You may, "but this is silly, this is like brain-in-vat arguments, these are not worthwhile to consider as a realistic model for things," and the answer is "sure! don't produce cosmological models that would have more brain vats than real people in them."

LE4dGOLEM: What's a Doug?Noc: A larval Doogly. They grow the tail and stinger upon reaching adulthood.

doogly wrote:Of course we're talking about a single mind. You can't claim to have independent observations of other things besides your mind, can you?

You may, "but this is silly, this is like brain-in-vat arguments, these are not worthwhile to consider as a realistic model for things," and the answer is "sure! don't produce cosmological models that would have more brain vats than real people in them."

I think you're missing my point - my question/issue is "are we claiming that many trillions of BBs are more likely than a creation event?" If the answer is 'No', then it does not seem to me to be reasonable to propose that a lower number of BBs could ever give rise to a mind with a fully-realised but non-existent history. Sure, it's 'possible', but my airport analogy stands...

How can I think my way out of the problem when the problem is the way I think?

That then raises the question of refining our definition of “creates more”—do we consider the creation of a small number N minds which then reproduce P offspring as being the same probability as the de novo creation of N+P minds? For example, positing a small number of original humans who were the ancestors of the estimated 100 billion humans who have existed to date—is that considered to be closer to the probability of the creation of the first generation of ancestors, or closer to the probability of the creation of the entire hundred billion together? My opinion is that it more resembles the former than the latter.

The thing is, brains tend to be significantly smaller than the entire universe. Ultimately, this is an argument about entropy, and a low entropy universe is much, much less probable than a low entropy brain no matter how it is arranged. Consider that in reality, your extremely improbable brain did evolve in the process of the universe approaching thermodynamic equilibrium; that is, the apparently stupendously unlikely creation was just a tiny eddy in the larger churning waters of the universe. There is no interpretation in which the entire universe arising out of a random fluctuation is more probable than a single mind.

But can we reasonably be talking about a single mind, given the elaborate, consistent, but completely fictional history contained in, e.g., mine? It's like setting off a bomb in a junkyard, and not only creating an airplane, but an airport, custom officers, security, runways, supporting infrastructure and manufacturers, and so on. How many bombs in how many junkyards do we need to set off before that becomes a plausible result? And at what point, does that number become less likely than an anti-entropic, essentially unstructured and disorganised, creation event?

For one thing, your mind might not have an elaborate, consistent history. It might just have a couple simple memories and the illusion of complexity. But even if we did suppose the Boltzmann brain were at least as complex as your real brain, that would still be very likely. Again, your brain did arise randomly out of the whole universe. Of course, it took a while, but the creation of such a universe by pure chance with no explanation for why it happened that particular way is still less likely than a brain being created by pure chance. The point is that any good model needs to give more constraints on the way the universe started than just "statistical fluctuation."

Anyway, I think you are underestimating the sizes of the numbers we are discussing here. It may be unlikely that a bomb in a junkyard would rearrange it into an airport, but it is far less likely that a bomb in a junkyard would make it all colder. There are simply so many more particles involved, even if it doesn't seem as "special" to us.

elasto wrote:That's why I claim life is special. It didn't take a bomb to create our entire civilisation including aircraft, runways, and a TSA enforcing a 100ml limit on liquids, 'all' it took was ten billion years

ijuin wrote:That then raises the question of refining our definition of “creates more”—do we consider the creation of a small number N minds which then reproduce P offspring as being the same probability as the de novo creation of N+P minds?

You don't calculate the chance of an organic brain appearing. You calculate the chance of some low-entropy configuration to appear (like a big bang event) and then you do a ballpark estimate of the amount of organic brains spawned by that configuration before it disappears or re-merges with thermal equilibrium.

Our observable universe has spawned or will spawn between 1 and 1e1000 sentient organic brains before its heat death - that number is accurate enough. If you worry about 10 orders of magnitude somewhere, then you've completely missed the point.

Things do get a bit tricky for theories that predict an infinite amount of either kind of brain.

Tub explained it much better than I could. The important caveat is that the brain doesn't have to just appear on its own immediately after the rare event; it could be a much later consequence of it. And we know for sure that real brains are a consequence of the real universe we have, so in order to find a "Boltzmann brain," we merely have to imagine a smaller universe that also evolves brains. This doesn't obviously lead to the conclusion that a brain in a vacuum is more probable than an evolved brain according to the history of our actual universe, but I think some more sophisticated analysis should reach that conclusion. But even if it doesn't, the problem remains.

That seems like it re-frames the problem as "big universes* are less likely to spontaneously arise than small ones". If we can also say (as seems intuitively plausible to me at least) that big universes are more likely to develop brains in them than small ones, it seems like the problem goes away: yeah, small universes the size of a brain are way way way more likely than great big universes like ours seems to be, but they're also way way way less likely to develop brains in them. A universe the size of a brain that consists of nothing but a brain is as unlikely as it sounds; most universes that size don't have brains in them, and most brains are found in bigger universes.

*(By which I mean regions of improbably low entropy embedded in a much larger, more entropic substrate).

That doesn't resolve the problem, as big universes are still more likely to develop one or more Boltzmann brains than the types of brains we consider. Even if the total population of brains over the course of history is 10^10^10, the Boltzmann brains will still outnumber them.

I think a segue of the conversation got lost. You were talking about how BBs don't have to just pop fully formed out of nothing, but can just arise as a consequent feature of a spontaneous low-energy event, like the one our universe is supposed by some to have come from, but smaller and more probable. The universe-proper (or multiverse if you like) spontaneously falls into a low-entropy state in one region, and that low-entropy state evolves over time and eventually gives rise to a brain, but not on the kind of scale that our universe is supposed to have. I was (as I said in my footnote) referring to such spontaneous low-energy events as "universes". A classical BB just popping out of nothing is then just one particular type of very small "universe", on the low end of a scale from non-notable micro-fluctuations on up to the kind of spontaneous low-entropy state our universe is supposed to have come from and beyond. If very small "universes" -- small spontaneous drops in entropy -- are less likely to evolve brains in them than large ones, counting "starting fully-formed as nothing but a brain" as a far edge case of "evolving" one, then we would expect most brains to be found in large universes.

Rather than resort to statistical improbabilities, wouldn't it be a better starting point to hypothesise a small, localised fluctuation in entropy that acts as a seed for a wider disruption? TBH I'm still confused as to the whole basis of the argument (although someone posted a link to a pdf I keep meaning to read). If the universe started from a zero-dimensional point-source, then it seems pretty meaningless to talk about probabilities in the first place.

How can I think my way out of the problem when the problem is the way I think?